Full duplex communication that simultaneously performs transmission and reception by using an identical frequency has been known. In full duplex communication, because the transmission and the reception are performed at the same time, self-interference in which the transmission signal of itself transmitted from a transmitting antenna sneaks into a receiving antenna of itself and results in an interference signal of the receiving signal occurs, and thereby the quality of the receiving signal is deteriorated. Consequently, the processing of cancelling the sneaking transmission signal by subtracting the transmission signal, which is output from a power amplifier, from the signal that is input into the receiving antenna is performed.
Furthermore, to suppress the self-interference, known has been a technology that controls the directivity of the transmitting antenna and the directivity of the receiving antenna so as not to spatially overlap with each other. Related-art examples are described in Japanese National Publication of International Patent Application No. 2013-526135, and in non-patent literature of H. Kawai, et al., “Independent Adaptive Control of Surviving Symbol Replica Candidates at Each Stage Based on Minimum Branch Metric in QRM-MLD for OFCDM MIMO Multiplexing,” IEEE VTC2004-Fall. Vol. 3, P 1558-1564.
Meanwhile, the transmission signal transmitted from the transmitting antenna may be reflected by an external obstacle and be input to the receiving antenna. Even when the directivity of the transmitting antenna and the directivity of the receiving antenna are controlled so as not to spatially overlap with each other, depending on the placement of the obstacle, the transmission signal transmitted from the transmitting antenna may be reflected by the obstacle and be input to the receiving antenna.
The signal that directly arrives at the receiving antenna from the transmitting antenna can be cancelled, based on the amount of attenuation and that of delay corresponding to the distance between the transmitting antenna and the receiving antenna, by subtracting the signal from a transmitting unit from the signal received by the receiving antenna. However, on the transmission signal that is reflected by the external obstacle and arrived at the receiving antenna, because the distance to the obstacle is unknown, the amount of attenuation and that of delay of the reflected waves that are input to the receiving antenna are unknown. Thus, in order to cancel the reflected waves by using the output from the power amplifier, a large scale circuit that performs the processing of estimating the reception strength and the delay of the reflected waves included in the received signal is to be provided. This makes the downsizing of the communication apparatus difficult.